1. Field of the Invention
This invention relates to the field of thermal reactors in integrated circuit fabrication, in particular, to the cleaning and purging of thermal reactors used for deposition of ruthenium metal and ruthenium compounds.
2. Statement of the Problem
Thin films of ruthenium, Ru, and ruthenium oxide, RuO2, are useful in integrated circuit devices and in fabrication of integrated circuits. Ruthenium and ruthenium oxide are generally useful as electrical contact materials. They have good electrical conductivity and show good environmental stability. They are useful for contact metallizations, diffusion barriers, and gate metallizations. Ruthenium oxide electrodes have shown utility as working electrodes in non-aqueous solvents. Ruthenium and ruthenium oxide are useful as capacitor electrodes that remain electrically conductive even after exposure to oxidizing conditions.
A thin film of ruthenium metal deposited on a wafer substrate is useful as a seed layer on which copper is deposited by electrochemical or electroless chemical plating techniques. Deposition of copper wiring in integrated circuits involves a number of processes. Typically, a trench or hole is etched into dielectric material located on a substrate wafer. The hole or trench then is typically lined with one or several adhesion layers, for example, with tantalum nitride, TaN. The hole or trench then is lined with a thin layer of copper, Cu, that acts as a seed layer for electroplated copper. Thereafter, the hole or trench is filled with copper, typically by an electroplating process. In the past, adhesion layers and copper seed layers lining holes and trenches were deposited using conventional physical vapor deposition techniques. As the design density of integrated circuits increases, resulting in smaller dimensions of holes and trenches, it is generally more difficult to use physical vapor deposition to line holes and trenches with uniform and conformal thin films of integrated circuit material.
Thus, as the design density of integrated circuits increases, resulting in smaller design features and dimensions, deposition of ruthenium and ruthenium oxide thin films, as well as thin films of other materials, by physical vapor deposition techniques is often unsatisfactory for obtaining good quality, continuous, and conformal thin films. As a result, deposition of ruthenium metal, ruthenium oxide, and other metal compounds by chemical vapor deposition (“CVD”) and atomic layer deposition (“ALD”) is important for achieving good circuit quality and acceptable manufacturing yields.
Techniques for depositing ruthenium metal, ruthenium oxide, and other ruthenium compounds by CVD and ALD have been developed for forming thin films on a surface of a semiconductor substrate or substrate assembly, such as a silicon wafer, having significant surface-area topology, such as high-aspect-ratio openings. For example, U.S. Pat. No. 6,074,945, issued Jun. 13, 2000, to Vaartstra et al., U.S. Pat. No. 5,372,849, issued Dec. 13, 1994, to McCormick et al., and U.S. Patent Application Publication No. U.S. 2003/0037802 A1, published Feb. 27, 2003, naming Nakahara et al., which are hereby incorporated by reference, disclose methods and precursors for CVD deposition of ruthenium and ruthenium oxide on integrated circuit substrates. CVD techniques for depositing ruthenium or ruthenium oxide typically utilize a hot-substrate hot-wall reactor apparatus to avoid condensation of reactant precursors prior to their decomposition at the substrate surface. Nevertheless, various suitable reaction apparati also include cold-wall/hot-substrate reactors, radiation beam reactors, and plasma-and photo-assisted CVD reactors.
A common problem in CVD and in ALD reactor apparati, especially but not only in hot-wall reactors, is the undesired formation of a CVD film deposit on reactor walls, tubing walls, and other apparatus surfaces. As a result, periodic in situ cleaning of apparatus surfaces to remove the undesired deposits is necessary. If these chamber cleans are not performed, then solid deposits typically delaminate from the apparatus walls, leading to particle contamination of wafer surfaces. The presence of particles decreases circuit integrity and lowers manufacturing yields. In situ cleaning of CVD and ALD reaction chambers and apparatus surfaces typically is accomplished by introducing gas-phase species that react with an undesired film deposit to form a volatile product. For example, fluorine atoms generated in a remote plasma source react with solid TiN and solid TaN to form volatile TiFx and TaFx species, respectively, which desorb from a surface and are pumped away. In the case of Ru, however, Ru does not form volatile fluorides, chlorides, bromides, or iodides. U.S. Patent Application Publication No. U.S. 2003/0037802 A1, published Feb. 27, 2003, naming Nakahara et al., discloses a method for removing a deposit of ruthenium metal or an oxide of ruthenium from the surfaces of a CVD apparatus by combining etching techniques using an oxygen-atom donating gas to clean a low-temperature surface, and a halogen-containing gas to clean high-temperature surfaces. The oxygen-atom donating gas is preferably ozone, and a halogen-containing gas is, for example, hydrogen fluoride or chlorine fluoride. Activated oxygen species, such as O-radicals and ozone, react with Ru metal deposits to form RuO4, an oxide of Ru that is volatile at room temperature. Nevertheless, RuO4 is a highly reactive, toxic, and carcinogenic compound.
The problem of toxic byproducts is not unique. Many byproducts of chamber cleaning processes are toxic; for example, hydrogen fluoride, HF. Nevertheless, readily available techniques for detecting common toxic byproducts exist and are used. In the case of RuO4, however, the toxicity problem is exacerbated because there is no practical and readily available method to detect this compound.